------- Additional Comments From steven at gcc dot gnu dot org 2004-11-20 17:01 ------- I have the following in the .optimized dump: flow_bb_inside_loop_p (loop, source_loop) { unsigned char D.1171; struct loop * D.1170; struct loop * * D.1169; struct loop * * D.1168; unsigned int D.1167; unsigned int D.1166; struct loop * * D.1165; int D.1164; int D.1163; int iftmp.0; int D.1161; struct loop * outer; struct loop * loop; unsigned char D.1146; unsigned char D.1145; int iftmp.1; int D.1140; int D.1160; # BLOCK 0 # PRED: ENTRY [100.0%] (fallthru,exec) if (loop == source_loop) goto <L8>; else goto <L0>; # SUCC: 6 [10.4%] (true,exec) 1 [89.6%] (false,exec) # BLOCK 1 # PRED: 0 [89.6%] (false,exec) <L0>:; D.1164 = loop->depth; if (source_loop->depth <= D.1164) goto <L4>; else goto <L1>; # SUCC: 4 [50.0%] (true,exec) 2 [50.0%] (false,exec) # BLOCK 2 # PRED: 1 [50.0%] (false,exec) <L1>:; if (loop != *(source_loop->pred + (struct loop * *) ((unsigned int) D.1164 * 4))) goto <L4>; else goto <L2>; # SUCC: 4 [81.0%] (true,exec) 3 [19.0%] (false,exec) # BLOCK 3 # PRED: 2 [19.0%] (false,exec) <L2>:; iftmp.0 = 1; goto <bb 7> (<L14>); # SUCC: 7 [100.0%] (fallthru,exec) # BLOCK 4 # PRED: 1 [50.0%] (true,exec) 2 [81.0%] (true,exec) <L4>:; iftmp.0 = 0; # SUCC: 7 [100.0%] (fallthru) # BLOCK 7 # PRED: 4 [100.0%] (fallthru) 3 [100.0%] (fallthru,exec) <L14>:; if ((unsigned char) (int) (unsigned char) iftmp.0 != 0) goto <L8>; else goto <L7>; # SUCC: 6 [33.0%] (true,exec) 5 [67.0%] (false,exec) # BLOCK 5 # PRED: 7 [67.0%] (false,exec) <L7>:; iftmp.1 = 0; goto <bb 8> (<L15>); # SUCC: 8 [100.0%] (fallthru,exec) # BLOCK 6 # PRED: 0 [10.4%] (true,exec) 7 [33.0%] (true,exec) <L8>:; iftmp.1 = 1; # SUCC: 8 [100.0%] (fallthru) # BLOCK 8 # PRED: 6 [100.0%] (fallthru) 5 [100.0%] (fallthru,exec) <L15>:; return (int) (unsigned char) iftmp.1; # SUCC: EXIT [100.0%] } Control flow graph: ENTRY | 0 |\ | \ 1 \ |\ \ | \ \ 2 \ \ |\ | | | \| | 3 4 | | / | |/ | 7 / |\ / | \ / 5 6 | / |/ 8 | EXIT Dominator tree: 0 /|\ 6 8 1 /|\ 4 7 2 | | 5 3 The problematic part is here: # BLOCK 3 # PRED: 2 [19.0%] (false,exec) <L2>:; iftmp.0 = 1; goto <bb 7> (<L14>); # SUCC: 7 [100.0%] (fallthru,exec) # BLOCK 4 # PRED: 1 [50.0%] (true,exec) 2 [81.0%] (true,exec) <L4>:; iftmp.0 = 0; # SUCC: 7 [100.0%] (fallthru) # BLOCK 7 # PRED: 4 [100.0%] (fallthru) 3 [100.0%] (fallthru,exec) <L14>:; if ((unsigned char) (int) (unsigned char) iftmp.0 != 0) goto <L8>; else goto <L7>; # SUCC: 6 [33.0%] (true,exec) 5 [67.0%] (false,exec) Possible causes of the missed jump thread: 1) Are casts getting in the way? 2) Do we need that one of edges into the condition we want to thread through dominates the block?
-- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18576